Fix some typos, broken links and other issues in extension docs

chrome/common/extensions/docs/templates/intros/pageCapture.html

 <p>
 The pageCapture API allows you to save a tab as MHTML.
 </p>
 
 <p>
 MHTML is a <a href="http://tools.ietf.org/html/rfc2557">standard format</a>
 supported by most browsers. It encapsulates in a single file a page and all
 its resources (CSS files, images..).
 </p>
 
 <p>
 Note that for security reasons a MHTML file can only be loaded from the file
 system and that it can only be loaded in the main frame.
 </p>
 
 <h2 id="manifest">Manifest</h2>
 
 
 <p>You must declare the "pageCapture" permission
 in the <a href="manifest.html">extension manifest</a>
-to use the history API.
+to use the pageCapture API.

[not at google - send to devlin, 2013/02/11 14:06:46]

$ref:pageCapture

[方觉(Fang Jue), 2013/02/12 03:27:14]

Other API docs don't use $ref here (since the target of the link is the same
page).

 For example:</p>
 <pre>{
   "name": "My extension",
   ...
   <b>"permissions": [
     "pageCapture"
   ]</b>,
   ...
-}</pre>
+}</pre>